Field emission displays (FED's) are well known in the art. A field emission display includes an anode plate and a cathode plate that define a thin envelope. Electron emitters are disposed on the cathode plate and conduct an electron emission current to the anode plate. To control the electron emission current, ballast resistors are provided between the electron emitters and the cathodes. The ballast resistors function to limit the electron emission current through each of the electron emitters. The FED generally requires high resistivity ballast resistors as part of the cathode design. The high resistivity materials used for ballast resistors are generally characterized by a large resistivity change as a function of temperature of the field emission display and cathode plate. In addition, the resistivity change is generally not linear with temperature. This results in a very dramatic change in electron emission current over temperature for the FED, and consequently, a dramatic change in brightness of the FED over temperature.
Also, the ballast resistors do not have identical temperature vs. resistance characteristics from FED to FED. The lack of consistent temperature vs. resistance characteristics of ballast resistors from FED to FED prevents accurate adjustment of electron emission current using conventional temperature sensing elements and circuitry.
Presently, temperature sensing elements can include a thermistor or pn junction, along with complex circuitry to assist in measuring the temperature of the FED and adjusting the electron emission current as a function of the temperature of the FED. However, this combination fails to consistently match the temperature vs. resistance characteristics of the field emission display or the ballast resistors. The result is a field emission display with a variation of brightness over changes in temperature.
Accordingly, there exists a need for a method of adjusting electron emission current in a field emission display for variations in temperature.